readme.txt
HiWinGS 2013, Fixed Riegl Lidar Wave Data
BWB, Mar 01, 2016

This directory contains 10-minute summary wave statistics and spectra computed from the
fixed-beam Riegl lidar deployed on the bow tower of R/V Knorr for the Davis Strait and
HiWinGS 2013 cruises.

Note, Riegl wave data is only available for julian dates 258 to 301.

Results are on a 10-minute timebase.  Nothing is computed for hours when data is missing or
loss is 100%.

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Variance spectra aree computed from the motion-corrected surface displacement timeseries
        with missing data interpolation (pchip).  The time series is high-pass filtered
        (0.04 Hz stopband, 0.05 Hz passband).  Spectra are only computed for 10-min
        intervals where data loss is < 50%.

Smoothed spectral data is saved as an Nx241 array in HiWinGS_2013_WaveSpectra.txt 
with the following format:

columns     variable                description
1           Decimal Day-of-Year     timestamp
2:79        Freq                    Frequency bin array, Hz
80:157      Df                      Delta F for bins, Hz
158:235     Sw                      Binned spectral data, m^2/Hz

See wave_specreader_HiWinGS_2013.m for code to read & plot from this file.


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10 minute wave stats file HiWinGS_2013_WaveStats_Hw_hdr.txt contains missing data count and
wave stats in the following format:

column    Description
1         jd Decimal Day-of-Year timestamp
2         # missing points in each 10 min segment
3         Hs from crude motion correction (-range + heave), m
4         Hs_cf from CF motion correction method, m
5         Hs_spec from spectral moment (4*sqrt(m0)), m
6         Tz mean zero crossing period from spectral moments (sqrt(m0/m2))
7         Te energy period from spectral moments (mn1/m0)
8         Tpc approximate wave peak period from spectral moments (mn2.*m1)./(m0^2)
9         m0 spectral moment (sum(S.*df))
10        m1 spectral moment (sum(f.*S.*df))
11        m2 spectral moment (sum((f.^2).*S.*df))
12        m3 spectral moment (sum((f.^3).*S.*df))
13        m4 spectral moment (sum((f.^2).*S.*df))
14        mn1 spectral moment (sum((f.^-1).*S.*df))
15        mn2 spectral moment (sum((f.^-2).*S.*df))
16        Fp frequency of highest spectral peak in 0.03-0.3 Hz band, Hz
17        Tp peak period = (1/Fp), sec
18        Fw estimated separation frequency for wind sea
19        U10n 10m neutral windspeed from COARE 3.5
20        Hw estimated significant wave ht for wind sea

Notes:
1) Variable 3, Hs, is computed as 4*std(h), where h is the crudely corrected surface
    displacement timeseries ( -lidar_range + heave ).  Heave is derived from the NOAA
    flux system motion correction.  Computed for every interval with data.
2) Variable 4, Hs_cf, is computed as 4*std(hc), where hc is corrected for pitch, roll
    and mount angle in addition to heave.  Computed for every interval with data.
3) Variable 5, Hs_spec, is computed as 4*sqrt(m0).  Probably the best value for times
    when spectra are computed.  Not computed when missing >50%.
4)	Fw and Hw are computed with assumption that U10n/Cp > 0.8 for wind sea equilibrium,
	thus Cp = U10n/0.8 and Fw = 0.8*g / (2*pi*U10n).  Hw is computed from the binned
	spectra (Swv), frequency bins (fwv) and delta frequency (dfw) as:
				ii = find(fwv>=Fw,1,'first'); % start bin for integrations
				hw = 4*sqrt(sum(Swv(ii:end).*dfw(ii:end)));